A multi-chip module (MCM) is broadly defined as any advanced semiconductor substrate which provides an interconnect path between electrical components mounted thereon. The electrical components are predominantly unpackaged integrated circuits, but may also comprise discrete circuit components such as resistors, capacitors, inductors, transistors and diodes.
With the arrival of higher speed computer processors, e.g. 66 megahertz and greater, the need to accelerate other computer functions has become evident. The slower speed of the memory bus and other peripherals, such as a coprocessor, limit the overall performance of the computer system and restrict the benefits to be gained from the higher speed processor. The incorporation of peripheral functions onto multi-chip modules provides a method for increasing the speed of those operations. However, as the processor and other component clock speeds are increased, the signal path length between processor and supporting active elements becomes more critical. Shorter distances between processor and the active elements will improve total system throughput. One way to achieve extremely close spacing is to package the die in a three dimensional fashion using internal layers within an MCM. This approach could be used for microprocessor to cache memory (SRAM) or any other bare die interconnect where path length is critical for sustaining rapid execution of processor instructions.